The invention is concerned with a loom having at least two sectional warp beams and a tension beam or roller for guiding warp threads running off the sectional warp beams. Each sectional warp beam is coupled to an individually drivable warp let-off motion device and sensors are provided for detecting the tension in the warp threads. Further, control equipment sets the r.p.m. of the sectional warp beams individually.
Such a loom, known from the EP patent 0 136 389, has sensors for the detection of the warp thread tension arranged between a stationary deflector for the warp threads, in the form of a rod connected after the sectional warp beams in the direction of run of the warp threads, and a tension roller which is arranged to pivot on a support beam parallel with the axis of the sectional warp beams. When weaving off two or more sectional warp beams each is driven individually in dependence upon control signals from the sensors at an r.p.m. selected so that all of the warp threads running off the sectional warp beams have essentially equal warp thread tensions. Any difference in the tension of the warp threads running off the sectional warp beams is immediately compensated for by appropriately changing the r.p.m. of the sectional warp beams.
In another known loom the tension roller is supported in bearings which are movable transversely to its axis and allow an oblique position of the tension roller with respect to the axis of the warp beam. Sensors associated with the ends of the tension roller enable an equalization of different warp thread tensions in the warp threads running off the sectional warp beams (German patent 27 58 816 and U.S. Pat. No. 4,262,706).
It has been found that such a regulation of the r.p.m. of the sectional warp beams, which is dependent only upon the tension of the warp threads, is not always adequate for achieving the same appearance in each of the lengths of cloth being woven off the sectional warp beams and thereby a quality of fabric which is constant across the whole width of weaving. In particular in the case of looms having high weft insertion capacities and/or having different diameters of the sectional warp beams it may happen that in spite of keeping the warp thread tension constant in the sectional warp sheets, the sectional warp beams are not woven off at the same time. Thus, sections of cloth with different lengths may be produced and/or separate sections of cloth may have a non-homogeneous appearance, in which case a seam or fold may form between the separate sections of cloth because of an unequal length of the separate sections.